Abstract
Dissolved organic carbon (DOC) from Oa horizons has been proposed to be an important contributor for subsoil organic carbon stocks. We investigated the fate of DOC by directly injecting a DOC solution from 13C labelled litter into three soil depths at beech forest sites. Fate of injected DOC was quantified with deep drilling soil cores down to 2 m depth, 3 and 17 months after the injection. 27 ± 26% of the injected DOC was retained after 3 months and 17 ± 22% after 17 months. Retained DOC was to 70% found in the first 10 cm below the injection depth and on average higher in the topsoil than in the subsoil. After 17 months DOC in the topsoil was largely lost (− 19%) while DOC in the subsoil did not change much (− 4.4%). Data indicated a high stabilisation of injected DOC in the subsoils with no differences between the sites. Potential mineralisation as revealed by incubation experiments however, was not different between DOC injected in topsoil or subsoils underlining the importance of environmental factors in the subsoil for DOC stabilisation compared to topsoil. We conclude that stability of DOC in subsoil is primary driven by its spatial inaccessibility for microorganisms after matrix flow while site specific properties did not significantly affect stabilisation. Instead, a more fine-textured site promotes the vertical transport of DOC due to a higher abundance of preferential flow paths.
Highlights
IntroductionR. Mikutta Faculty of Natural Sciences III, Martin-Luther-University Halle-Wittenberg, Von-Seckendorff-Platz 3, 06120 Halle, Germany between 27 and 77% of soil organic carbon (SOC) in mineral soils (Harrison et al 2011; Rumpel and KogelKnabner 2011)
Subsoils have been recognised as an overlooked key component of the terrestrial carbon pool, containingP
Quantitative data on the contribution and turnover of different compounds such as dissolved organic carbon (DOC) entering subsoils are scarce (Kogel-Knabner 2017) The results from two synthesis papers showed that the input of DOC into forest subsoils is much higher than the output via leaching which means that a considerable portion of DOC is retained or mineralised in the subsoil (Kindler et al 2011; Michalzik et al 2001)
Summary
R. Mikutta Faculty of Natural Sciences III, Martin-Luther-University Halle-Wittenberg, Von-Seckendorff-Platz 3, 06120 Halle, Germany between 27 and 77% of soil organic carbon (SOC) in mineral soils (Harrison et al 2011; Rumpel and KogelKnabner 2011). Forest soils represent an important component of the global C cycle, due to their higher C stocks as compared to arable soils (Poeplau et al 2011). Beside roots, dissolved organic carbon (DOC) is a major source of fresh carbon (C) that enters subsoils (Kaiser and Guggenberger 2000). Kalbitz and Kaiser (2008) estimated the contribution of DOC to the subsoil C stock of a Podzol to be in the range of 25–66% for the B and C horizon. Consequent questions are inter alia: what is the origin of this DOC, how does it reach subsoils and what drives its stability if it is stable at all?
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